1. Field of the Invention
This invention relates to refrigerating systems and more particularly to a defrost pressure control system employed in refrigerating systems for facilitating easier starting of the compressor of such refrigerating systems after a defrosting operation.
2. Description of the Prior Art
Refrigerating systems, particularly those used with household refrigerators, usually include a compressor driven by an electric motor of relatively small horsepower. Moreover, the motor usually has a low starting torque, particularly since, for reasons of economy, such motors employed with present day household refrigerators normally do not include a capacitor start winding. When the pressure in such a refrigerating system has equalized during and at the end of a defrosting cycle, the pressure which has to be overcome by the compressor in its initial stroke may be such that the force required exceeds the starting torque of the electric motor which drives the compressor.
The present invention is directed to an improvement associated with such refrigerating systems which insures that the required starting torque does not exceed that which is available from the driving electric motor. This is accomplished by providing a reservoir associated in a particular manner with the refrigerating system for causing a portion of the refrigerant in the system to be withdrawn therefrom to the reservoir in liquid form during the defrosting operation, thereby reducing the amount of refrigerant in the system, and hence the pressure thereof, when the compressor starts after the conclusion of the defrosting operation. This reduces the force which must be exerted by the piston of the compressor during its initial stroke after defrosting and hence correspondingly reduces the starting torque required of the electric motor which drives the compressor.
The prior art includes numerous examples of reservoirs associated with refrigerating systems, such reservoirs being designed to contain a portion of the refrigerant under certain operating conditions. However, none of these prior art devices of which the applicants are aware disclose an arrangement in which the reservoir is specifically provided to withdraw liquid refrigerant from the system during a defrosting operation for the purpose of facilitating the starting of the compressor at the conclusion of the defrosting operation.
Thus, the prior art includes, for example, heat pump systems wherein refrigerant is removed from the system when the heat pump is used for heating purposes and returned to the system when the heat pump is used for cooling, because less refrigerant is needed during the heating cycle. None of these systems, however, involve any consideration of defrosting nor of the problems of starting a compressor after defrosting nor of the desirability of reducing pressure in the refrigerating system to facilitate starting of the compressor after defrosting.
Another example of a prior art system utilizing a reservoir connected with a refrigerating system places the reservoir in a location where the temperature is above normal and uses it while the refrigerating compressor is running rather than idle. Therefore, it does not consider the problem of starting a compressor, which is the specific problem solved by the applicants' system; it is not concerned with defrosting; and, as will be explained later in the specification, the applicants' system requires that the reservoir be placed where the temperature is below that existing in the refrigerating system during defrosting.
Another prior art system utilizing a reservoir connected with the refrigerating system includes a sight glass in the reservoir and is intended to be used to determine whether the proper refrigerant charge is being maintained in the system. It is concerned in no way with withdrawing refrigerant during defrosting so as to make restarting of the compressor at the termination of the defrosting operation easier.
Another prior art system incorporating a reservoir is arranged so that refrigerant is stored therein during normal operation and released from storage during defrosting, exactly the opposite of that required for effective operation of the applicants' system.
Other prior art refrigerating systems including an associated reservoir have utilized such a reservoir in order to provide a means for varying the refrigerant in the system in order to vary the effective condenser surface or the number of a plurality of capillaries effectively utilized in the system. The systems disclosed were not concerned with defrosting nor with the problem of starting a compressor after defrosting. Moreover, these particular systems required an electric heater associated with the reservoir to drive refrigerant from the reservoir.
In contrast to the above-described prior art systems, none of which is concerned with defrosting and the problem of start-up of the compressor after a defrosting operation, the applicants' system provides a simple and effective arrangement for automatically removing a substantial portion of refrigerant from the refrigerating system and storing it in a reservoir in liquid form during defrosting. Thus, the total pressure in the system at the end of the defrosting operation is reduced and the torque required of the electric motor in starting the compressor after defrosting is substantially reduced. The problem of failure of the motor to provide sufficient torque to start the compressor after defrosting is eliminated. Further, in the applicants' system, the stored refrigerant is automatically and promptly returned to the refrigerating system as soon as normal operation has been resumed after conclusion of the defrosting operation.
Accordingly, it is an object of this invention to provide a defrost pressure control system which facilitates easy starting of the refrigerant compressor after a defrosting operation.
It is another object of this invention to provide a defrost pressure control system by which the amount of refrigerant in the system is automatically reduced during defrosting to facilitate easier starting of the compressor after the defrosting operation is completed and by which the stored refrigerant is automatically returned to the refrigerating system when normal operation of the system is resumed.